This invention relates to data communication systems and, more particularly, to a data communication system of the type comprising a communicating medium, a plurality of transceivers connected to the medium, and means for interrupting the transmission of data onto the medium by one transceiver when that same transceiver receives data transmitted by another transceiver.
An example of a data communications system of the above-type is disclosed in U.S. Pat. No. 4,063,220. As described in that patent, a collision detector is provided with each transceiver for detecting when the data on the medium differs from the data being communicated by the associated transceiver. A detected difference indicates a "collision" between the signal being transmitted by the associated transceiver and a signal from another transceiver. In response to the detected collision, a collision signal is generated. This signal is then sensed by appropriate means to interrupt transmission by the associated transceiver.
As also described in U.S. Pat. No. 4,063,220, data received by a transceiver connected to the communicating medium is forwarded to a phase decoder which basically separates the data and clock components of the received data. Both data and clock component signals are then respectively applied to the data and clock inputs of a shift register. The shift register converts the serial input data stream into parallel data words of predetermined bit-length, e.g., 16-bit words for transmittal through a synchronizing buffer register onto a data bus for transfer to a using device.
It would be desirable if the need for a separate collision detector for each transceiver could be eliminated, thereby reducing the number of components and the overall complexity of the system. It would also be desirable if the phase decoder were completely digital in design, unlike the phase decoder disclosed in U.S. Pat. No. 4,063,220, which contains analog components. As is well known analog components tend to drift out of adjustment. Further, a completely digital phase decoder is more amemable to microelectronic integration.